Phoenix (/ ˈ f iː n ɪ k s /) is the capital and most populous city of Arizona, with 1,626,000 people (as of 2017).It is also the fifth most populous city in the United States, and the most populous American state capital, and the only state capital with a population of more than one million residents.. Phoenix is the anchor of the Phoenix metropolitan area, also known as the Valley of the …